If You Think the Weather Is Bad . . .

Weather is almost impossible to predict more than a week or two in advance. But when it comes to climate -- the long-term weather averages that make the U.S. temperate and the tropics torrid -- scientists are confident that they understand the overall pattern. Over the past million years or so, the planet has swung between ice ages lasting on the order of 100,000 years and interglacial periods of about 10,000. During each phase, the climate is pretty steady. It's the stability of the current interglacial epoch, which began 10,000 years ago, that made the invention of agriculture, and thus the...